Run certain bit of code at ANY time?

I'm creating a prop bomb and the 7 segment display is controlled by a 74HC595 Shift Register. I wan't to run a "defuse" code when a button is pressed, but I don't want to put:
if(val == 1){Serial.println("defused");} on every single line, besides, doing that will only read it every second or so. Is there a way to run a function always no matter what?

Yes, it's called not using delay() in your sketches.

I have to do that for the seven segment display to count down...

Yes so you do your line:-

if(val == 1){Serial.println("defused");}

once at the start of the loop() function and write the rest of the code so that the loop() repeats very quickly.

The thing is, it HAS to be a one second delay for the countdown.

it HAS to be a one second delay for the countdown.

But that doesn't mean the loop() has to run at this rate. See the blink without delay example already in your arduino IDE for how to use the millis() counter to time action.

I don't under stand how I can modify the blink without delay code...

I don't under stand how I can modify the blink without delay code.

When you start the countdown, observe what value millis() returns. On each pass though loop, see if now (obtained by calling millis()) minus then (when the display value was last changed, as when starting the bomb) is greater than, or equal to, one second. If it is, change the displayed value and reset the time that the display value was changed. Otherwise, do nothing.